Frequency Question

[Aethis]

All right, this is a newbie question, I'm sure. I've been looking over the Epoch, and have found out there just doesn't seem to be a lot of information about it on the net... perhaps I'm searching under the wrong things, but I've not been able to had this question answered: How many epochs can you have racing at once, and what dictates the frequency each car is on? I've seen the 'frequency crystals' they have, but I've never seen 'extras' sold, for different frequencies. Does it come with 4 different types, or something? Is there a switch to go from channel to channel?

Thanks in advance for the help.